This invention relates to electrical machinery and, more particularly, to an improved rotor assembly for AC generators.
AC generators are often used for various applications. For example, a generator may be mechanically coupled to and driven by a constant speed drive unit which provides rotational energy to the rotor of the generator at a constant speed. Alternatively, the generator may be coupled to an auxiliary power unit. When an AC generator is coupled to a selected constant speed drive or auxiliary power unit to form a power system, it is typical in such a system to circulate oil through the generator for lubricating and cooling. Generally, oil enters the generator through one end of a hollow rotor shaft from an oil supply. The oil flows through the shaft and out its other end. The oil pressure at each end of the hollow rotor shaft should be substantially the same.
The hollow rotor shaft carries the field winding structure and the rectifier assembly for rectifying the voltage from the exciter windings. The shaft is provided with holes through which oil flows for lubricating and cooling portions of the generator. For example, holes may be located near the field winding structure so that an oil spray from the holes impinges upon end turns of the field winding structure for cooling. Also, holes may be provided near the rectifier assembly for cooling the diodes in the assembly. Moreover, holes through which oil flows may be placed along the shaft for lubricating selected portions, as for example, a splined end of the shaft of the generator which receives the constant speed drive or the auxiliary power unit.
The volume of oil flow through the holes in the hollow rotor shaft should be maintained at a selected level for optimum operation. Furthermore, the velocity of the oil spray from the holes should be controlled to minimize erosion of the insulation on end turn windings of the field winding structure.
Different constant speed drives and auxiliary power units have different oil inlet pressures and oil flow requirements which must be maintained. Therefore, before an AC generator is coupled to a particular constant speed drive or auxiliary power unit, the rotor must often be disassembled and the diameter and number of the holes in the hollow rotor shaft must be changed to assure that the oil inlet pressures and oil flow requirements are matched so that the constant speed drive or auxiliary power unit and the AC generator cooperate effectively with each other. Rotor disassembly and replacement is time-consuming and expensive.